This invention relates to two-terminal Hall sensors and their use in magnetic field monitoring systems, and more particularly pertains to a monitoring systems with fault detection and diagnostic capabilities wherein each of a plurality of remote Hall sensors are connected by two conductors to a sensors-addressing and control module.
A two terminal Hall sensor is described in the U.S. Pat. No. 4,374,333 to Grant Avery, issued Feb. 15, 1983 and assigned to the same assignee as is the present invention. This integrated circuit Hall sensor includes an on-board voltage regulator and the output stage is a current source providing an output current of predetermined value when the ambient magnetic field exceeds a prescribed value and no output current otherwise.
Such two terminal Hall sensors are employed in a vehicle monitoring system that is described in the U.S. Pat. No. 4,791,311 to Ravi Vig, issued Dec. 13, 1988 and assigned to the same assignee as is the present invention. These remote multiplexible two-terminal Hall sensors are all connected in parallel along a single pair of conductors and to a control module that addresses each sensor in sequence by multiplexing signals; the wiring is greatly simplified whereas the sensors must be multiplex-addressable.
The system of the present invention is intended for building security systems and vehicle monitoring tasks wherein simplicity and reliability are foremost considerations, and distinguishes from the multiplexing system in U.S. Pat. No. 791,311 by employing a plurality of simple switching two-terminal Hall sensors, e.g. as described in U.S. Pat. No. 4,374,333 each Hall sensor being connected to the control module by its own wire(s).
It is an object of this invention to provide such a vehicle monitoring system that uses a simple control module for switching from one Hall sensor to the next and for detecting and decoding in each Hall sensor the output current to determine whether a fault exists between the control module and the sensor and if not whether the magnetic field strength exceeds a certain value there.